1. Technical Field
The inventive arrangements relate generally to methods and apparatus providing advanced operating features for audio only, video only and both video and audio programs recorded on disc media, for example recordable digital video discs, hard drives and magneto optical discs.
2. Description of the Related Art
Various devices have been developed to enable consumers to record video and/or audio programs for later presentation. Such devices include tape recorders, video cassette recorders, recordable compact discs, and most recently, recordable digital video discs (DVD). Hard drives and magneto optical discs have also been used.
A DVD that can be recorded on only once, and thereafter is essentially a DVD read only memory, is referred to by the acronym DVD-R. The acronym DVD-R is also used generally to refer to the write-once, or record-once, technology. Several formats are available for DVD's to be recorded on, erased and re-recorded; that is, overwritten or rewritten. These are referred to by the acronyms DVD-RAM, DVD-RW and DVD+RW. As of this time no uniform industry standard has been adopted. The acronyms DVD-RAM, DVD-RW and DVD+RW are also used generally to refer to the respective rewritable technologies. Reference herein to rewritable DVD technology, devices and methods is generally intended to encompass all of the standards which are now being used, as well as those which may be developed in the future.
In many cases, the program presentations are recorded in the viewer's absence for presentation at a later, more convenient time. This is referred to as time shifting the program. At other times, the viewer may be called away while he is watching a program that is not being recorded. If the viewer owns a conventional video cassette recorder, the viewer may begin recording the program during the interruption. The viewer, however, must wait until the program is completed to watch the remainder of the program in a proper time sequence. A further complication is that the time to complete the recording can be excessive depending on the length of the broadcast. This can result in the viewer ignoring the interruption or missing significant portions of the program.
To overcome this problem, a DVD video recorder can incorporate a pause feature. When activated, this setting, similar to other conventional video recording machines, allows the viewer to record incoming video. Significantly, however, when the pause-resume feature is activated, the DVD video recorder jumps back to that portion of the program where the pause was initiated to commence playback yet the recorder continues to record incoming video. As a result, the viewer, if interrupted for any number of reasons, can watch a program in its entirety without having to wait for the original broadcast to end.
Although it may appear to be simultaneous, the DVD recorder cannot read and write data at the same time. Thus, to achieve seamless playback and recording, the DVD recorder must alternate between recording data on the disc and reading this data. The time allotted for either reading or writing data is determined, at least in part, by the limited size of the DVD recorder's read and write data buffers. As a consequence, the recorder must constantly switch between reading and writing to avoid buffer overflow or underflow.
Typically, if the DVD recorder's read and write data buffers have a capacity of roughly 2.1 Mbytes and the bit rate is at a maximum bit rate of 8.35 Mbits/sec, then the DVD recorder can have a capacity that provides approximately two seconds for one reading or writing step plus the time required to position the DVD recorder's read/write head. For example, once a writing step is completed, the DVD recorder has around two seconds to move its read/write head into the proper reading position, read a portion of data and then move its read/write head back to perform another writing step. After that time, if the DVD recorder is not designed properly, then buffer underflow and/or overflow may occur. The foregoing timing assumes the bit rate is at a maximum of 8.35 Mbits/sec. Under normal operating conditions, a properly designed DVD recorder can achieve seamless playback and recording, even at this maximum bit rate. Significantly, however, if the system is required to operate in a trick mode while the forgoing reading and writing is taking place, certain problems may occur due to the faster consumption of data stored in the buffers and/or additional data reading requirements. In particular, the DVD recorder runs the risk of losing data from overflowing the writing data buffer due to the increased time spent reading data.
During the reading steps, the writing data buffer receives and stores data to be written onto the disc. Once a reading step is completed, the DVD recorder will shift its read/write head back to a position on the disc to begin another writing step thereby allowing the writing buffer to empty. If the DVD recorder receives a trick mode command, it commonly will be necessary to read additional data from the disc. However, as the reading step is nearing completion and the writing buffer is nearing capacity, the DVD recorder will not extend the reading step to perform the trick mode. Instead, the DVD recorder will move its read/write head to begin the writing step to prevent writing buffer overflow. As a result, the viewer will experience a delay in the initiation of the trick mode.
Further compounding the problem is the additional time required to read during a trick mode. Since the DVD recorder skips pictures during certain trick modes such as fast-forward or fast-reverse, the DVD recorder must read a greater amount of data during the reading steps to compensate for the faster speed at which these pictures are processed. Thus, the DVD recorder must spend a significant amount of time reading data to prevent underfiow of the reading buffer. In response to the lengthier reading steps, it may be desirable to have the DVD recorder empty the writing buffer before initiating a trick mode, even if the data in the buffer is substantially lower than maximum capacity. This additional writing step can increase the system response time for performing the trick mode. This problem can be particularly significant where a video segment contains relatively high bit rates.
A similar user response time problem can occur when, during a pause-resume mode, a user causes the system to discontinue playback of the current program and instead play back video from another location on the disc. In this case, it may again be desirable to empty the writing buffer before beginning the reading step, which can result in a delay.
In order to overcome the delay in response time caused by performing a writing step before beginning a trick mode, a second writing buffer can be implemented into the DVD recorder. Adding such a buffer would allow the DVD recorder to initiate trick modes with no delay because any excess data from the first writing buffer would merely overflow into the second writing buffer. This solution, however, is not entirely satisfactory because adding a second buffer increases the costs of the DVD recorder and increases the DVD recorder's bus load. Thus, what is needed is an approach which accommodates the additional write data which can accumulate during the pause-resume mode so as not to increase user response time, but without incurring significant additional expense and bus load.